The present invention relates to thermoplastic polymer compositions comprising particulate vulcanized rubber, a thermoplastic material and at least one coupling agent.
The environmental problems created by discarded tires are significant and growing in such proportions that landfills are often refusing to accept tires and governmental agencies are searching for solutions. Due to the lack of successful commercial projects that utilize discarded tires, there are an estimated two billion discarded tires in the United States alone. In addition to this, estimates are that 240 to 300 million tires will be discarded annually. Many of the current uses for discarded tires either raise serious environmental issues or have such limited commercial feasibility that they make no significant impact on the problem.
Attempts have been made to reclaim vulcanized rubber for decades but mainly for the purpose of de-vulcanizing in order to have once again a processable rubber. This technology generally involves taking particulate vulcanized rubber and defiberizing it, and treating it with combinations of chemicals, steam heat and/or considerable mechanical working to reduce molecular weight and thereby enable the resultant material to be processed and re-vulcanized as a conventional rubber product. The reclaimed rubber so produced is then blended with virgin rubber or used directly depending on the particular technique used and the end product to be made. Examples of these techniques can be seen in U.S. Pat. Nos. 2,783,213 and 2,966,468.
The use of particulate vulcanized rubber as an ingredient in thermoplastic compounds is very limited. U.S. Pat. No. 3,489,710 describes how to manufacture a composition of devulcanized rubber with selected polymers to create a reconstituted rubber product. A disadvantage of this process is that it requires a devulcanization step for the rubber and therefore appears to be limited to rubber products. U.S. Pat. No. 4,341,667 relates to a composition of microwave devulcanized rubber and select polymers. The primary disadvantage of this process is the cost associated with devulcanization and limited usefulness.
Various additive compounds have been used in compositions of vulcanized rubber polymers. These compounds have included surfactants such as those set forth in U.S. Pat. No. 4,386,182 and liquid low molecular weight polymers such as those set forth in U.S. Pat. No. 4,481,335.
There is still a need for processable compositions of vulcanized rubber and thermoplastic materials which exhibit excellent overall toughness and strength. There is also a need for plastic-rubber compositions which can be processed in a relatively simple and economic technique without having to devulcanize the particulate rubber.
Accordingly, it is an object of the present invention to provide plastic-rubber compositions having utility in producing high quality non-rubber thermoplastic products as well as cross-linked products and rubber products.
It is a further object of the present invention to provide plastic-rubber compositions as above having excellent physical properties.
It is yet a further object of the present invention to provide a relatively simple and economic process for producing the above plastic-rubber compositions.
These and other objects and advantages will become more apparent from the following description.